// DeflaterHuffman.cs
//
// Copyright (C) 2001 Mike Krueger
// Copyright (C) 2004 John Reilly
//
// This file was translated from java, it was part of the GNU Classpath
// Copyright (C) 2001 Free Software Foundation, Inc.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
// 
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module.  An independent module is a module which is not derived from
// or based on this library.  If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so.  If you do not wish to do so, delete this
// exception statement from your version.

using System;
using ICSharpCode.SharpZipLib.Zip.Compression;

namespace ICSharpCode.SharpZipLib.Zip.Compression
{
    /// <summary>
    /// This is the DeflaterHuffman class.
    /// 
    /// This class is <i>not</i> thread safe.  This is inherent in the API, due
    /// to the split of Deflate and SetInput.
    /// 
    /// author of the original java version : Jochen Hoenicke
    /// </summary>
    public class DeflaterHuffman
    {
        const  int BUFSIZE = 1 << (DeflaterConstants.DEFAULT_MEM_LEVEL + 6);
        const  int LITERAL_NUM = 286;

        // Number of distance codes
        const  int DIST_NUM = 30;
        // Number of codes used to transfer bit lengths
        const  int BITLEN_NUM = 19;

        // repeat previous bit length 3-6 times (2 bits of repeat count)
        const  int REP_3_6    = 16;
        // repeat a zero length 3-10 times  (3 bits of repeat count)
        const  int REP_3_10   = 17;
        // repeat a zero length 11-138 times  (7 bits of repeat count)
        const  int REP_11_138 = 18;

        const  int EOF_SYMBOL = 256;

        // The lengths of the bit length codes are sent in order of decreasing
        // probability, to avoid transmitting the lengths for unused bit length codes.
        static readonly int[] BL_ORDER = { 16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15 };
		
        static readonly byte[] bit4Reverse = {
                                                 0,
                                                 8,
                                                 4,
                                                 12,
                                                 2,
                                                 10,
                                                 6,
                                                 14,
                                                 1,
                                                 9,
                                                 5,
                                                 13,
                                                 3,
                                                 11,
                                                 7,
                                                 15
                                             };

        static readonly short[] staticLCodes;
        static readonly byte[]  staticLLength;
        static readonly short[] staticDCodes;
        static readonly byte[]  staticDLength;
		
        class Tree 
        {
            #region Instance Fields
            public readonly short[] freqs;
			
            public byte[]  length;
			
            public readonly int     minNumCodes;
			
            public int     numCodes;
			
            short[] codes;
            readonly int[]   bl_counts;
            readonly int     maxLength;
            readonly DeflaterHuffman dh;
            #endregion

            #region Constructors
            public Tree(DeflaterHuffman dh, int elems, int minCodes, int maxLength) 
            {
                this.dh =  dh;
                minNumCodes = minCodes;
                this.maxLength  = maxLength;
                freqs  = new short[elems];
                bl_counts = new int[maxLength];
            }
			
            #endregion

            /// <summary>
            /// Resets the internal state of the tree
            /// </summary>
            public void Reset() 
            {
                for (int i = 0; i < freqs.Length; i++) {
                    freqs[i] = 0;
                }
                codes = null;
                length = null;
            }
			
            public void WriteSymbol(int code)
            {
                //				if (DeflaterConstants.DEBUGGING) {
                //					freqs[code]--;
                //					//  	  Console.Write("writeSymbol("+freqs.length+","+code+"): ");
                //				}
                dh.pending.WriteBits(codes[code] & 0xffff, length[code]);
            }

            /// <summary>
            /// Set static codes and length
            /// </summary>
            /// <param name="staticCodes">new codes</param>
            /// <param name="staticLengths">length for new codes</param>
            public void SetStaticCodes(short[] staticCodes, byte[] staticLengths)
            {
                codes = staticCodes;
                length = staticLengths;
            }
			
            /// <summary>
            /// Build dynamic codes and lengths
            /// </summary>
            public void BuildCodes() 
            {
                var nextCode = new int[maxLength];
                var code = 0;

                codes = new short[freqs.Length];
				
                //				if (DeflaterConstants.DEBUGGING) {
                //					//Console.WriteLine("buildCodes: "+freqs.Length);
                //				}
				
                for (int bits = 0; bits < maxLength; bits++) {
                    nextCode[bits] = code;
                    code += bl_counts[bits] << (15 - bits);

                    //					if (DeflaterConstants.DEBUGGING) {
                    //						//Console.WriteLine("bits: " + ( bits + 1) + " count: " + bl_counts[bits]
                    //						                  +" nextCode: "+code);
                    //					}
                }	
                for (int i=0; i < numCodes; i++) {
                    int bits = length[i];
                    if (bits > 0) {

                        //						if (DeflaterConstants.DEBUGGING) {
                        //								//Console.WriteLine("codes["+i+"] = rev(" + nextCode[bits-1]+"),
                        //								                  +bits);
                        //						}

                        codes[i] = BitReverse(nextCode[bits-1]);
                        nextCode[bits-1] += 1 << (16 - bits);
                    }
                }
            }
			
            public void BuildTree()
            {
                int numSymbols = freqs.Length;
				
                /* heap is a priority queue, sorted by frequency, least frequent
				* nodes first.  The heap is a binary tree, with the property, that
				* the parent node is smaller than both child nodes.  This assures
				* that the smallest node is the first parent.
				*
				* The binary tree is encoded in an array:  0 is root node and
				* the nodes 2*n+1, 2*n+2 are the child nodes of node n.
				*/
                var heap = new int[numSymbols];
                var heapLen = 0;
                var maxCode = 0;
                for (var n = 0; n < numSymbols; n++) {
                    int freq = freqs[n];
                    if (freq == 0)
                    {
                        continue;
                    }

                    // Insert n into heap
                    var pos = heapLen++;
                    int ppos;
                    while (pos > 0 && freqs[heap[ppos = (pos - 1) / 2]] > freq) {
                        heap[pos] = heap[ppos];
                        pos = ppos;
                    }
                    heap[pos] = n;
						
                    maxCode = n;
                }
				
                /* We could encode a single literal with 0 bits but then we
				* don't see the literals.  Therefore we force at least two
				* literals to avoid this case.  We don't care about order in
				* this case, both literals get a 1 bit code.
				*/
                while (heapLen < 2) {
                    int node = maxCode < 2 ? ++maxCode : 0;
                    heap[heapLen++] = node;
                }
				
                numCodes = Math.Max(maxCode + 1, minNumCodes);
				
                var numLeafs = heapLen;
                var childs = new int[4 * heapLen - 2];
                var values = new int[2 * heapLen - 1];
                var numNodes = numLeafs;
                for (var i = 0; i < heapLen; i++) {
                    var node = heap[i];
                    childs[2 * i]   = node;
                    childs[2 * i + 1] = -1;
                    values[i] = freqs[node] << 8;
                    heap[i] = i;
                }
				
                /* Construct the Huffman tree by repeatedly combining the least two
				* frequent nodes.
				*/
                do {
                    int first = heap[0];
                    int last  = heap[--heapLen];
					
                    // Propagate the hole to the leafs of the heap
                    int ppos = 0;
                    int path = 1;
					
                    while (path < heapLen) {
                        if (path + 1 < heapLen && values[heap[path]] > values[heap[path+1]]) {
                            path++;
                        }
							
                        heap[ppos] = heap[path];
                        ppos = path;
                        path = path * 2 + 1;
                    }
						
                    /* Now propagate the last element down along path.  Normally
					* it shouldn't go too deep.
					*/
                    int lastVal = values[last];
                    while ((path = ppos) > 0 && values[heap[ppos = (path - 1)/2]] > lastVal) {
                        heap[path] = heap[ppos];
                    }
                    heap[path] = last;
					
					
                    int second = heap[0];
					
                    // Create a new node father of first and second
                    last = numNodes++;
                    childs[2 * last] = first;
                    childs[2 * last + 1] = second;
                    int mindepth = Math.Min(values[first] & 0xff, values[second] & 0xff);
                    values[last] = lastVal = values[first] + values[second] - mindepth + 1;
					
                    // Again, propagate the hole to the leafs
                    ppos = 0;
                    path = 1;
					
                    while (path < heapLen) {
                        if (path + 1 < heapLen && values[heap[path]] > values[heap[path+1]]) {
                            path++;
                        }
							
                        heap[ppos] = heap[path];
                        ppos = path;
                        path = ppos * 2 + 1;
                    }
						
                    // Now propagate the new element down along path
                    while ((path = ppos) > 0 && values[heap[ppos = (path - 1)/2]] > lastVal) {
                        heap[path] = heap[ppos];
                    }
                    heap[path] = last;
                } while (heapLen > 1);
				
                if (heap[0] != childs.Length / 2 - 1) {
                    throw new SharpZipBaseException("Heap invariant violated");
                }
				
                BuildLength(childs);
            }
			
            /// <summary>
            /// Get encoded length
            /// </summary>
            /// <returns>Encoded length, the sum of frequencies * lengths</returns>
            public int GetEncodedLength()
            {
                int len = 0;
                for (int i = 0; i < freqs.Length; i++) {
                    len += freqs[i] * length[i];
                }
                return len;
            }
			
            /// <summary>
            /// Scan a literal or distance tree to determine the frequencies of the codes
            /// in the bit length tree.
            /// </summary>
            public void CalcBLFreq(Tree blTree) 
            {
                var curlen = -1;             /* length of current code */
                var i = 0;

                while (i < numCodes) {
                    var count = 1;                   /* repeat count of the current code */
                    int nextlen = length[i];
                    int max_count;               /* max repeat count */
                    int min_count;               /* min repeat count */
                    if (nextlen == 0) {
                        max_count = 138;
                        min_count = 3;
                    } else {
                        max_count = 6;
                        min_count = 3;
                        if (curlen != nextlen) {
                            blTree.freqs[nextlen]++;
                            count = 0;
                        }
                    }
                    curlen = nextlen;
                    i++;
					
                    while (i < numCodes && curlen == length[i]) {
                        i++;
                        if (++count >= max_count) {
                            break;
                        }
                    }
					
                    if (count < min_count) {
                        blTree.freqs[curlen] += (short)count;
                    } else if (curlen != 0) {
                        blTree.freqs[REP_3_6]++;
                    } else if (count <= 10) {
                        blTree.freqs[REP_3_10]++;
                    } else {
                        blTree.freqs[REP_11_138]++;
                    }
                }
            }
		
            /// <summary>
            /// Write tree values
            /// </summary>
            /// <param name="blTree">Tree to write</param>
            public void WriteTree(Tree blTree)
            {
                var curlen = -1;             // length of current code
				
                var i = 0;
                while (i < numCodes) {
                    var count = 1;                   // repeat count of the current code
                    int nextlen = length[i];
                    int max_count;               // max repeat count
                    int min_count;               // min repeat count
                    if (nextlen == 0) {
                        max_count = 138;
                        min_count = 3;
                    } else {
                        max_count = 6;
                        min_count = 3;
                        if (curlen != nextlen) {
                            blTree.WriteSymbol(nextlen);
                            count = 0;
                        }
                    }
                    curlen = nextlen;
                    i++;
					
                    while (i < numCodes && curlen == length[i]) {
                        i++;
                        if (++count >= max_count) {
                            break;
                        }
                    }
					
                    if (count < min_count) {
                        while (count-- > 0) {
                            blTree.WriteSymbol(curlen);
                        }
                    } else if (curlen != 0) {
                        blTree.WriteSymbol(REP_3_6);
                        dh.pending.WriteBits(count - 3, 2);
                    } else if (count <= 10) {
                        blTree.WriteSymbol(REP_3_10);
                        dh.pending.WriteBits(count - 3, 3);
                    } else {
                        blTree.WriteSymbol(REP_11_138);
                        dh.pending.WriteBits(count - 11, 7);
                    }
                }
            }

            void BuildLength(int[] childs)
            {
                length = new byte [freqs.Length];
                var numNodes = childs.Length / 2;
                var numLeafs = (numNodes + 1) / 2;
                var overflow = 0;
				
                for (var i = 0; i < maxLength; i++) {
                    bl_counts[i] = 0;
                }
				
                // First calculate optimal bit lengths
                var lengths = new int[numNodes];
                lengths[numNodes-1] = 0;
				
                for (int i = numNodes - 1; i >= 0; i--) {
                    if (childs[2 * i + 1] != -1) {
                        int bitLength = lengths[i] + 1;
                        if (bitLength > maxLength) {
                            bitLength = maxLength;
                            overflow++;
                        }
                        lengths[childs[2 * i]] = lengths[childs[2 * i + 1]] = bitLength;
                    } else {
                        // A leaf node
                        var bitLength = lengths[i];
                        bl_counts[bitLength - 1]++;
                        length[childs[2*i]] = (byte) lengths[i];
                    }
                }
				
                //				if (DeflaterConstants.DEBUGGING) {
                //					//Console.WriteLine("Tree "+freqs.Length+" lengths:");
                //					for (int i=0; i < numLeafs; i++) {
                //						//Console.WriteLine("Node "+childs[2*i]+" freq: "+freqs[childs[2*i]]
                //						                  + " len: "+length[childs[2*i]]);
                //					}
                //				}
				
                if (overflow == 0) {
                    return;
                }
				
                int incrBitLen = maxLength - 1;
                do {
                    // Find the first bit length which could increase:
                    while (bl_counts[--incrBitLen] == 0)
                    {

                    }

                    // Move this node one down and remove a corresponding
                    // number of overflow nodes.
                    do {
                        bl_counts[incrBitLen]--;
                        bl_counts[++incrBitLen]++;
                        overflow -= 1 << (maxLength - 1 - incrBitLen);
                    } while (overflow > 0 && incrBitLen < maxLength - 1);
                } while (overflow > 0);
				
                /* We may have overshot above.  Move some nodes from maxLength to
				* maxLength-1 in that case.
				*/
                bl_counts[maxLength-1] += overflow;
                bl_counts[maxLength-2] -= overflow;
				
                /* Now recompute all bit lengths, scanning in increasing
				* frequency.  It is simpler to reconstruct all lengths instead of
				* fixing only the wrong ones. This idea is taken from 'ar'
				* written by Haruhiko Okumura.
				*
				* The nodes were inserted with decreasing frequency into the childs
				* array.
				*/
                int nodePtr = 2 * numLeafs;
                for (int bits = maxLength; bits != 0; bits--) {
                    int n = bl_counts[bits-1];
                    while (n > 0) {
                        int childPtr = 2*childs[nodePtr++];
                        if (childs[childPtr + 1] == -1) {
                            // We found another leaf
                            length[childs[childPtr]] = (byte) bits;
                            n--;
                        }
                    }
                }
                //				if (DeflaterConstants.DEBUGGING) {
                //					//Console.WriteLine("*** After overflow elimination. ***");
                //					for (int i=0; i < numLeafs; i++) {
                //						//Console.WriteLine("Node "+childs[2*i]+" freq: "+freqs[childs[2*i]]
                //						                  + " len: "+length[childs[2*i]]);
                //					}
                //				}
            }
			
        }

        #region Instance Fields
        /// <summary>
        /// Pending buffer to use
        /// </summary>
        public DeflaterPending pending;

        readonly Tree literalTree;
        readonly Tree distTree;
        readonly Tree blTree;
		
        // Buffer for distances
        readonly short[] d_buf;
        readonly byte[]  l_buf;
        int last_lit;
        int extra_bits;
        #endregion

        static DeflaterHuffman() 
        {
            // See RFC 1951 3.2.6
            // Literal codes
            staticLCodes = new short[LITERAL_NUM];
            staticLLength = new byte[LITERAL_NUM];

            int i = 0;
            while (i < 144) {
                staticLCodes[i] = BitReverse((0x030 + i) << 8);
                staticLLength[i++] = 8;
            }

            while (i < 256) {
                staticLCodes[i] = BitReverse((0x190 - 144 + i) << 7);
                staticLLength[i++] = 9;
            }

            while (i < 280) {
                staticLCodes[i] = BitReverse((0x000 - 256 + i) << 9);
                staticLLength[i++] = 7;
            }

            while (i < LITERAL_NUM) {
                staticLCodes[i] = BitReverse((0x0c0 - 280 + i)  << 8);
                staticLLength[i++] = 8;
            }
			
            // Distance codes
            staticDCodes = new short[DIST_NUM];
            staticDLength = new byte[DIST_NUM];
            for (i = 0; i < DIST_NUM; i++) {
                staticDCodes[i] = BitReverse(i << 11);
                staticDLength[i] = 5;
            }
        }
		
        /// <summary>
        /// Construct instance with pending buffer
        /// </summary>
        /// <param name="pending">Pending buffer to use</param>
        public DeflaterHuffman(DeflaterPending pending)
        {
            this.pending = pending;
			
            literalTree = new Tree(this, LITERAL_NUM, 257, 15);
            distTree    = new Tree(this, DIST_NUM, 1, 15);
            blTree      = new Tree(this, BITLEN_NUM, 4, 7);
			
            d_buf = new short[BUFSIZE];
            l_buf = new byte [BUFSIZE];
        }

        /// <summary>
        /// Reset internal state
        /// </summary>		
        public void Reset() 
        {
            last_lit = 0;
            extra_bits = 0;
            literalTree.Reset();
            distTree.Reset();
            blTree.Reset();
        }
		
        /// <summary>
        /// Write all trees to pending buffer
        /// </summary>
        /// <param name="blTreeCodes">The number/rank of treecodes to send.</param>
        public void SendAllTrees(int blTreeCodes)
        {
            blTree.BuildCodes();
            literalTree.BuildCodes();
            distTree.BuildCodes();
            pending.WriteBits(literalTree.numCodes - 257, 5);
            pending.WriteBits(distTree.numCodes - 1, 5);
            pending.WriteBits(blTreeCodes - 4, 4);
            for (int rank = 0; rank < blTreeCodes; rank++) {
                pending.WriteBits(blTree.length[BL_ORDER[rank]], 3);
            }
            literalTree.WriteTree(blTree);
            distTree.WriteTree(blTree);
        }

        /// <summary>
        /// Compress current buffer writing data to pending buffer
        /// </summary>
        public void CompressBlock()
        {
            for (int i = 0; i < last_lit; i++) {
                int litlen = l_buf[i] & 0xff;
                int dist = d_buf[i];
                if (dist-- != 0) {
                    //					if (DeflaterConstants.DEBUGGING) {
                    //						Console.Write("["+(dist+1)+","+(litlen+3)+"]: ");
                    //					}
					
                    int lc = Lcode(litlen);
                    literalTree.WriteSymbol(lc);
					
                    int bits = (lc - 261) / 4;
                    if (bits > 0 && bits <= 5) {
                        pending.WriteBits(litlen & ((1 << bits) - 1), bits);
                    }
					
                    int dc = Dcode(dist);
                    distTree.WriteSymbol(dc);
					
                    bits = dc / 2 - 1;
                    if (bits > 0) {
                        pending.WriteBits(dist & ((1 << bits) - 1), bits);
                    }
                } else {
                    //					if (DeflaterConstants.DEBUGGING) {
                    //						if (litlen > 32 && litlen < 127) {
                    //							Console.Write("("+(char)litlen+"): ");
                    //						} else {
                    //							Console.Write("{"+litlen+"}: ");
                    //						}
                    //					}
                    literalTree.WriteSymbol(litlen);
                }
            }
            literalTree.WriteSymbol(EOF_SYMBOL);
        }
		
        /// <summary>
        /// Flush block to output with no compression
        /// </summary>
        /// <param name="stored">Data to write</param>
        /// <param name="storedOffset">Index of first byte to write</param>
        /// <param name="storedLength">Count of bytes to write</param>
        /// <param name="lastBlock">True if this is the last block</param>
        public void FlushStoredBlock(byte[] stored, int storedOffset, int storedLength, bool lastBlock)
        {
            pending.WriteBits((DeflaterConstants.STORED_BLOCK << 1) + (lastBlock ? 1 : 0), 3);
            pending.AlignToByte();
            pending.WriteShort(storedLength);
            pending.WriteShort(~storedLength);
            pending.WriteBlock(stored, storedOffset, storedLength);
            Reset();
        }

        /// <summary>
        /// Flush block to output with compression
        /// </summary>		
        /// <param name="stored">Data to flush</param>
        /// <param name="storedOffset">Index of first byte to flush</param>
        /// <param name="storedLength">Count of bytes to flush</param>
        /// <param name="lastBlock">True if this is the last block</param>
        public void FlushBlock(byte[] stored, int storedOffset, int storedLength, bool lastBlock)
        {
            literalTree.freqs[EOF_SYMBOL]++;
			
            // Build trees
            literalTree.BuildTree();
            distTree.BuildTree();
			
            // Calculate bitlen frequency
            literalTree.CalcBLFreq(blTree);
            distTree.CalcBLFreq(blTree);
			
            // Build bitlen tree
            blTree.BuildTree();
			
            int blTreeCodes = 4;
            for (int i = 18; i > blTreeCodes; i--) {
                if (blTree.length[BL_ORDER[i]] > 0) {
                    blTreeCodes = i+1;
                }
            }
            int opt_len = 14 + blTreeCodes * 3 + blTree.GetEncodedLength() + 
                          literalTree.GetEncodedLength() + distTree.GetEncodedLength() + 
                          extra_bits;
			
            int static_len = extra_bits;
            for (int i = 0; i < LITERAL_NUM; i++) {
                static_len += literalTree.freqs[i] * staticLLength[i];
            }
            for (int i = 0; i < DIST_NUM; i++) {
                static_len += distTree.freqs[i] * staticDLength[i];
            }
            if (opt_len >= static_len) {
                // Force static trees
                opt_len = static_len;
            }
			
            if (storedOffset >= 0 && storedLength + 4 < opt_len >> 3) {
                // Store Block

                //				if (DeflaterConstants.DEBUGGING) {
                //					//Console.WriteLine("Storing, since " + storedLength + " < " + opt_len
                //					                  + " <= " + static_len);
                //				}
                FlushStoredBlock(stored, storedOffset, storedLength, lastBlock);
            } else if (opt_len == static_len) {
                // Encode with static tree
                pending.WriteBits((DeflaterConstants.STATIC_TREES << 1) + (lastBlock ? 1 : 0), 3);
                literalTree.SetStaticCodes(staticLCodes, staticLLength);
                distTree.SetStaticCodes(staticDCodes, staticDLength);
                CompressBlock();
                Reset();
            } else {
                // Encode with dynamic tree
                pending.WriteBits((DeflaterConstants.DYN_TREES << 1) + (lastBlock ? 1 : 0), 3);
                SendAllTrees(blTreeCodes);
                CompressBlock();
                Reset();
            }
        }
		
        /// <summary>
        /// Get value indicating if internal buffer is full
        /// </summary>
        /// <returns>true if buffer is full</returns>
        public bool IsFull()
        {
            return last_lit >= BUFSIZE;
        }
		
        /// <summary>
        /// Add literal to buffer
        /// </summary>
        /// <param name="literal">Literal value to add to buffer.</param>
        /// <returns>Value indicating internal buffer is full</returns>
        public bool TallyLit(int literal)
        {
            //			if (DeflaterConstants.DEBUGGING) {
            //				if (lit > 32 && lit < 127) {
            //					//Console.WriteLine("("+(char)lit+")");
            //				} else {
            //					//Console.WriteLine("{"+lit+"}");
            //				}
            //			}
            d_buf[last_lit] = 0;
            l_buf[last_lit++] = (byte)literal;
            literalTree.freqs[literal]++;
            return IsFull();
        }
		
        /// <summary>
        /// Add distance code and length to literal and distance trees
        /// </summary>
        /// <param name="distance">Distance code</param>
        /// <param name="length">Length</param>
        /// <returns>Value indicating if internal buffer is full</returns>
        public bool TallyDist(int distance, int length)
        {
            //			if (DeflaterConstants.DEBUGGING) {
            //				//Console.WriteLine("[" + distance + "," + length + "]");
            //			}
			
            d_buf[last_lit]   = (short)distance;
            l_buf[last_lit++] = (byte)(length - 3);
			
            int lc = Lcode(length - 3);
            literalTree.freqs[lc]++;
            if (lc >= 265 && lc < 285) {
                extra_bits += (lc - 261) / 4;
            }
			
            int dc = Dcode(distance - 1);
            distTree.freqs[dc]++;
            if (dc >= 4) {
                extra_bits += dc / 2 - 1;
            }
            return IsFull();
        }

		
        /// <summary>
        /// Reverse the bits of a 16 bit value.
        /// </summary>
        /// <param name="toReverse">Value to reverse bits</param>
        /// <returns>Value with bits reversed</returns>
        public static short BitReverse(int toReverse) 
        {
            return (short) (bit4Reverse[toReverse & 0xF] << 12 | 
                            bit4Reverse[(toReverse >> 4) & 0xF] << 8 | 
                            bit4Reverse[(toReverse >> 8) & 0xF] << 4 |
                            bit4Reverse[toReverse >> 12]);
        }
		
        static int Lcode(int length) 
        {
            if (length == 255) {
                return 285;
            }
			
            int code = 257;
            while (length >= 8) {
                code += 4;
                length >>= 1;
            }
            return code + length;
        }
		
        static int Dcode(int distance) 
        {
            int code = 0;
            while (distance >= 4) {
                code += 2;
                distance >>= 1;
            }
            return code + distance;
        }
    }
}